Home › Forum › Ask A Member › 1985 Evinrude 9.9 misfire
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davesko.
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May 10, 2018 at 3:04 am #9876
Hi all, So I picked up for 50.00 an 85 Evinrude 9.9 that was overheated. The guy said it started steaming and he shut it off. I did a compression test and got 96 top and 95 bottom so I proceeded to put in a new water pump, thermostat and head gasket sanding the head on a piece of glass with sandpaper on it to make sure it’s flat. Put it all back together and it starts very easily but could tell lower cylinder was not firing correctly so I once again checked spark and it was jumping a 3/4 gap but when the Top plug wire is pulled off it stalls. When I pull the bottom off it doesn’t stall but you can hear it run differently when taken off and put back on. Is it possible/probable that the cylinder or head is cracked letting water into the lower cylinder? Where should I go from here? Btw the overheat was caused by a stuck closed thermostat.
May 10, 2018 at 4:03 am #75665Do you have the model number handy for this engine? Either on the stern bracket or the chip in the powerhead? Do they match?
Dan in TN
May 10, 2018 at 4:07 am #75666Model number is E10RCOM and they do match
May 10, 2018 at 9:51 am #75668Usually the thermostats get stuck OPEN. You do know about the chronic 9.9/15 problem of water tube grommet restriction under the power head, right? When the motor has that condition, water will still come out of the tell tale fairly well, which fools a lot of owners.
If it is misfiring from water intrusion, you will usually be able to see evidence of it on the misfiring spark plug.
Long live American manufacturing!
May 10, 2018 at 1:04 pm #75675This thermostat was stuck closed, yes i know about the grommet.
May 10, 2018 at 2:42 pm #75683Well, the engine is new to you, so we don’t know how it ran prior to the overheat…
Just want to be sure I understand what you are reporting…You feel the engine is running on just one cylinder, the lower #2 is not firing properly for some reason…But, you feel the lower cylinder is sparking "OK" because you feel/hear some sort of response when the #2 plug wire is pulled, even though RPM doesn’t really change. Do I have it right?
Well, sure you could have a water leak, doubt the head is cracked though…And, like Bill says, you will probably be able to see water droplets on the plug when you remove it…
Have you tried to run the engine at higher speeds in gear? If so, does the #2 kick in, or does it continue to run on just the top cylinder.
I guess I would go back to step one after checking the lower plug for water. Will then spark jump 7/16-1/2" gap while cranking? If so, did you try different plugs? Just cuz they are new, doesn’t mean they are any good. If all seems OK so far, you might want to try monitoring running spark with a timing light or those inline neon testers. If all seems OK so far, you might want to check compression again, perhaps something happened between the time you checked compression and now.
I can’t remember which cylinder the fuel pump is plumbed into, seems like it is the top cylinder, so it is no likely that a leaky fuel pump diaphragm in affecting the lower cylinder. I suppose you might have a broken reed, but that wouldn’t be my first "guess" and I would recheck all the simpler options before ripping the intake manifold off…May 10, 2018 at 3:29 pm #75687Maybe a piece of dirt stuck in a reed holding it part way open?
DaveMay 10, 2018 at 3:39 pm #75689Hi Don, you have it correct. It not firing correctly on the bottom cylinder, when i do my drop test it does drop off a little and idles back up when put back on. I just did another compression test and got 96 top and 95 bottom and did another spark test and it will jump a 3/4 gap. i have not had it on a boat yet but will this weekend. Im going to get another set of plugs today and see what happens. I cant readily see any droplets of water on the plug and i know the cylinder head is flat,new gasket "sierra" if that matters and torqued correctly. Im also going to get one of those inline neon testers. I have many of the 9.9-15’s and i know what they should sound like and thats what prompted the drop test. Before i replaced the pump,head gasket and thermostat i ran it for a short time and the miss was not there, so it has to be something i did or that water flow was established to somewhere that wasnt getting water before. Thank you very much! Dave
May 10, 2018 at 8:57 pm #75712OK, well will it clear out and run up OK at WOT in gear? Or, is this just a problem at lower speeds….
Like I said, I "think" the fuel pump is plumbed into the upper cylinder but could be wrong…A leaky diaphragm could be fouling out the lower cylinder if I am wrong….You could test this theory by unplugging the fuel line and running the engine…If the engine cleans up and starts running right once fuel is pulled out of the line, then we can look into this theory a little more…
How do the plugs look? If the lower plug appears "wet", try tapping it on the palm of your hand…It might be easier to see water droplets this way…May 11, 2018 at 12:16 pm #75771Hi Don, Thanks for the info. Putting new plugs in today and going to take it out on the boat tonight. I will check the bottom plug after a run.
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